Butterfly nectaring flowers: butterfly morphology and flower form

The profitability of butterfly foraging depends in part on the corolla depth and clustering of flowers, and the tongue length, body mass and wing loading of butterflies. Interactions among these attributes of flowers and butterflies were investigated, using data from a field study in Cornwall and from Porter et al. (1992). The maximum corolla depth from which a butterfly can feed depends on tongue length, which correlates with the more easily measured attributes of body mass and wing loading. Small, short-tongued butterflies did not visit deep flowers. The quantity of nectar sugar per flower necessary for profitable foraging depends on foraging costs, which are expected to correlate with wing loading. Butterfly species with a high wing loading generally confined their visits to flowers that were clustered or very nectar-rich. Butterfly species with a low wing loading included solitary and less nectar-rich flowers in their diet. Body mass and wing loading affect a butterfly's load-carrying capacity (limiting the distance between fuelling stops) and cooling rate (limiting the distance between stops for basking or endothermic warming), and will therefore influence the capacity for floral selectivity and for migration and dispersal. Body mass, wing loading and tongue length characterised families or subfamilies of butterflies. For example vanessine nymphalids, with their long tongues and high wing loading, visited the deep, massed flowers of Buddleja davidii, but lycaenids, with their short tongues and low wing loading, did not. These often visited members of the Asteraceae. Eupatorium cannabinum, with massed flowers offering abundant and accessible nectar, was visited by butterflies of all tongue lengths and both high and low wing loading. These findings may help to inform habitat management for butterfly nectaring flowers.